CuII hydroxy salts: characterization of layered compounds by vibrational spectroscopy

Abstract

Hidroxo-sais lamelares de composição Cu 2 (OH) 3 X (X = NO 3 -, CH 3 COO -e ClO 4 -) foram sintetizados através da coprecipitação (sais básicos de nitrato e acetato) e da troca iônica (sal básico de perclorato). Os sólidos cristalinos foram caracterizados por difratometria de raios X, análise termogravimétrica e espectroscopia vibracional. Bandas fracas em 336 e 345 cm -1 (espectro Raman) dos sais de nitrato e perclorato, respectivamente, foram tentativamente atribuídas ao νCu-O (ânion). Os ions nitrato possuem simetria C 2v no composto Cu 2 (OH) 3 NO 3 e, consequentemente, observa-se o desdobramento dos modos E'. A quebra da degenerescência também é observada nos modos F 2 do íon ClO 4 -livre, ocasionando o desdobramento das bandas em 630 e 1100 cm -1 no espectro do hidroxo-perclorato de cobre(II). A pequena diferença de energia entre os modos ν as C-O e ν s C-O (Δ=143 cm -1 ) do sal de acetato sugere a presença de ligação de hidrogênio entre o oxigênio não coordenado do grupo carboxilato e um íon hidroxila adjacente. Os íons nitrato, acetato e perclorato estão coordenados ao cobre(II) de modo monodentado.Copper hydroxy salts with a layer-type structure and general composition Cu 2 (OH) 3 X (X = NO 3 -, CH 3 COO -and ClO 4 -) were synthesized by co-precipitation (nitrate and acetate salts) and ion exchange (perchlorate salt) methods. The isolated polycrystalline solids were characterized by X-ray diffractometry, thermogravimetric analysis and vibrational spectroscopy. A weak band at 336 and 345 cm -1 (Raman spectrum) of the nitrate and perchlorate salts, respectively, was tentatively assigned to the nCu-O (anion). In Cu 2 (OH) 3 NO 3 the nitrate ion has a C 2v symmetry and, accordingly, a splitting in the E' modes is observed. The same happens to the hydroxy perchlorate salt with the degeneracy breakdown of the F 2 modes (free ClO 4 -) at 630 and 1100 cm -1 leading to band splitting. For the carboxylate salt, the small difference in the energy of ν as C-O and ν s C-O (Δ=143 cm -1 ) suggests that hydrogen bonding with neighbor OH group may be present. Nitrate, carboxylate and perchlorate are monocoordinated to copper(II) in the investigated salts.

Anion Exchange Kinetics of Nanodimensional Layered Metal Hydroxides: Use of Isoconversional Analysis

“…The 001−003 Bragg reflections were used to calculate the basal spacing of BCN using the Bragg equation, 35 the obtained value of 6.94 ± 0.01 Å matches literature value of 6.81 Å. 36 (Table S1 in the Supporting Information). The metal ion to anion ratios are consistent, within approximately 10%, for a nearly 1:1 exchange.…”

“…The metal ion to anion ratios are consistent, within approximately 10%, for a nearly 1:1 exchange. 36,37 The presence of two O-NO2 peaks is consistent with vibrations of coordinated nitrate groups of C2v symmetry. Coordination of the nitrate group to the matrix copper ion through one of the oxygen atoms reduces the symmetry of the nitrate ion from D3h in free nitrate to C2v resulting in splitting of the doubly degenerate NO2 stretch (v3, 1360−1380 cm −1 ) in free nitrate.…”

Simple route for the synthesis of copper hydroxy salts

“…Generally, hydroxy salts are synthesized by one of the following methods: the pyrolysis of a metallic salt; 4 the reaction of a metallic oxide with the corresponding aqueous solution of a salt of the desired metal; 3-5 the slow precipitation of HS with sodium hydroxide from a metal salt solution; 4,8,11 the co-precipitation procedure employed for LDH synthesis, introduced by Newman and Jones. 4 Additionally, the reaction of a metal oxide (MeO) with zinc acetate in an aqueous media, was reported by Morioka et al 2 Some of these procedures demand strict control of experimental variables, especially pH, temperature and concentration of the reactants to avoid the formation of sub-products like Cu(OH) 2 and CuO.…”

“…It is naturally found in the mineral called Gerhardtite, but a stable monoclinic phase is obtained by conventional synthetic routes. [8][9][10] The structure of Cu 2 (OH) 3 NO 3 can be imagined as being obtained by replacement of 25% of the OH -anions in the cooper hydroxide sheets by NO 3 -anions directly coordinated to copper(II) cations through one of its oxygen atoms, as shown in Figure 1. The stacking of such a sheets in the z direction lead to the formation of a neutral threedimensional structure.…”

“…Metallic hydroxy salts with the composition M 2 (OH) 3 X (M = Cu, Co; X = organic anion) 5,8 have been extensively studied because of their interesting magnetic properties, that are strongly dependent on the structure and molecular ordering of intercalated anions, as well as, the interlayer distance determined by them. Accordingly, the properties of those materials can be easily manipulated, such that can be considered tunable magnetic materials. )…”